Simian virus 40 (SV40) and human cytomegalovirus (HCMV) activate the cell's metabolic and protein synthetic environment to support viral replication. They also induce cellular stress responses which would normally decrease metabolism and synthesis. We have shown that SV40 and HCMV have developed mechanisms to override stress responses. SV40 T antigen and HCMV major immediate early proteins (MIEPs) activate Akt kinase through activation of phosphatidylinositide 3'-OH kinase (PI3K). An advantage of activating Akt is activation of mTOR (mammalian target of rapamycin) kinase which activates cap-dependent translation. However, many cellular stress responses directly inactivate mTOR kinase, leading to inhibition of cap-dependent translation. We have shown that both HCMV and SV40 infections circumvent this inhibition, maintaining the phosphorylation of mTOR effectors despite stress or the presence of rapamycin, an mTOR inhibitor. HCMV's adaptation to growth in rapamycin is in part mediated by the specific phosphorylation status of the MIEPs. SV40 infection activates mTOR signaling early but diverges from HCMV during its late phase when mTOR effectors are specifically dephosphorylated, and cap-dependent translation is inhibited. We hypothesize that this favors the utilization of internal ribosome entry sites (IRESs) predicted to be in the polycistronic late mRNAs. Three aims are proposed: Aim 1: Determine the mechanism(s) by which HCMV infection circumvents mTOR inhibition through alterations of the mTOR complexes. We will characterize HCMV-induced alterations which impart novel capabilities to the mTOR-raptor and mTOR-rictor complexes. We will determine the makeup of the complexes in infected cells compared to uninfected cells and determine what viral proteins and cellular processes are involved in the process. Aim 2: Define the role of phosphorylation in the function of the HCMV MIEPs, particularly during adaptation to growth in rapamycin. Aim 2a. We will determine how hypophosphorylation of MAP kinase sites in IE2/IEP86 enables adaptation to growth in rapamycin;this connects Aim 2 with Aim 1. Aim 2b. We will continue to mutate, map and phenotypically characterize phosphorylation sites of IE2/IEP86 and IE1/IEP72. Aim 3. Determine the mechanism by which SV40 causes the hypophosphorylation of mTOR effectors late in infection to inhibit cap-dependent translation and how this relates to the utilization of IRESs for the production of late proteins. SV40 small t antigen mediates hypophosphorylation of mTOR effectors;this requires its ability to bind protein phosphatase 2a (PP2A). Aim 3a. Determine how t Ag is mediating the hypophosphorylation. Aim 3b. Detect and characterize IRESs in the SV40 late mRNAs.